Mobile telephones are an example of a battery-powered device familiar to most people. The extant battery life of battery-power devices, including mobile telephones, is of considerable importance to their users. Consequently, the provision of extant battery life indicators on mobile telephones is universal.
One method of determining the extant battery life of an apparatus, such as a mobile telephone, is to measure the battery voltage and then read an extant battery life value from a pre-programmed lookup table. This has the advantage of being relatively simple to implement but suffers from a lack of accuracy.
This problem is addressed in GB-A-2312517 which describes taking three voltage readings, fitting a discharge curve to the readings and then determining the extant battery life from the curve fitted to the readings. This approach is more accurate than the earlier lookup table technique.
However, the technical considerations for battery-powered apparatus include meeting users' expectations for the man-machine interface beyond merely providing information accurately. A problem therefore arises with the approach to extant battery life determination described in GB-A-2312517 in that the result is not available for several minutes after the first voltage reading is taken. This has been found to be unsatisfactory with users and the delay can be interpreted by users as indicating a “flat” battery.
The technique of GB-A-2312517 also may not respond quickly enough if the current drain on a battery is high, e.g. when a mobile telephone is in active mode.